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Liquid diffusion, mentioned previously as evidence of molecular motion, was investigated by Graham (1850-62). He placed small bottles containing solutions of various substances in large jars of water,
 | Fig: Grahams experiment on liquid diffusion |
and determined by analysis the amount of substance diffusing into the water in a given time.
By using apparatus of the same dimensions, he was able to obtain comparative results, and found that the rates of diffusion differed considerably. Acids and salts diffused fairly quickly, whereas glue, starch, and albumin diffused only very slowly. The rapidly diffusing substances were (except acids) all crystalline in the solid state, and were called crystalloids by Graham. Gum and albumin, however, form amorphous solid masses resembling glue, and were called colloids (Greek kolla, glue). The differences were so great that Graham considered himself justified in differentiating between "two worlds of matter, the crystalloid and the colloid," each with characteristic properties.
| Substance | Times of equal diffusion | Ammounts diffusing in equal times. | | Sodium chloride | 100 | 100 | | Ammonia | 160 | 85 | | Alcohol | 200 | 47 | | Glucose | 300 | 36 | | Gum arabic | 700 | 0.8 | | Albumin | 2100 | 0.3 |
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